How do I control the level of magnification to show only the areas I wish to map?

[SandraRice1]

I need to map Western NC's 25 counties, and would only like them to be visible on my view.  Is there a way to do this?

[RobertBorchert]

Create a data driven page that is the boundary of your 25 counties.

Set up data driven pages and clip to the Index Layer (ArcGIS Pro)

You can also make a large polygon,  Clip out the area where the 25 counties are and it will mask the other.

Now a super super cumbersome way that I had to do years ago was I assigned a County FIPS number to every single asset. (Electric Distribution). The system was in 6 counties. And then set up definition queries in each feature class to only show the needed ones. It works but I would avoid it. 

[SandraRice1]

Thanks Robert.  I will work on this tomorrow.